Disposable absorbent articles, which include sanitary napkins, catamenial pads, panty liners and the like, are designed to absorb the discharge of body fluids such as urine and blood from a wearer. These articles typically are multi-layered in construction and are comprised of a liquid-permeable cover sheet having one side designed for placement in contact with the wearer, an absorbent core for effecting storage of the discharged body fluids and a liquid impervious backsheet for retaining the stored fluids within the disposable absorbent article. In early disposable articles, the liquid-permeable cover was affixed to the absorbent core for permitting rapid transfer of body fluids down into the absorbent. In more recent years it has been common to include a transfer or distribution layer between the underside of the cover sheet and the absorbent core to facilitate transfer of fluids. The transfer sheet or distribution layer is highly porous and has wicking capability which essentially pulls body fluids through the cover sheet with direction toward the absorbent core.
The attachment of the cover sheet to the transfer layer or absorbent core throughout its surface is a necessary practice to insure that good fluid transfer takes place. Currently, commercial manufacturers of the absorbent articles employ hot melt adhesives and/or heated embossing rolls to attach the cover sheet to the distribution layer or absorbent core of the absorbent product to each other. These are applied to the sides of the absorbent core typically in a hairline patten. A problem with hot melt adhesives is that they can plug the apertures in the cover sheet. Another problem associated with the employment of hot melt adhesives is that additional equipment is required, e.g., an applicator which melts the adhesive and a spray assembly for each converting machine. The latter requires constant cleaning and dealing with the plugged nozzles. A problem with heated embossing rolls for attaching the cover sheet to the transfer layer is that both temperature and pressure control must be carefully monitored to avoid distortion and or melting of the cover sheet.
Another mechanism for attaching cover sheets formed from carded webs is the use of thermoplastic bicomponent fibers. These fibers melt at elevated temperature and fuse with the distribution layer or absorbent core. As with melt adhesives, the use of bicomponent fibers requires close temperature control to prevent plugging of pores, distortion, etc.
The application of self sealable binders, such as a pressure sensitive adhesive, applied to an absorbent core can promote some bonding between the cover sheet and the absorbent core at room temperature. However, making a commercial air-laid roll with this type of binder is very difficult since the binder tends to block and bond the entire web when the roll is wound onto large drums for storage. The only way to prevent this problem is to add a release liner between the plies which adds to the cost.
The following patents are representative of multi-layer constructed disposable absorbent products suited for the applications addressed.
U.S. Pat. No. 5,401,267 discloses an absorbent article having enhanced wicking capacity. The absorbent article is comprised of a liquid-permeable cover, a liquid-impermeable baffle, and an absorbent core disposed between the liquid-permeable cover and the liquid-impermeable baffle. The cover sheet is comprised of a perforated polyethylene film for permitting rapid transfer of fluid to the absorbent core. Disposed between the cover sheet is a distribution or transfer layer which has a lower wicking capacity than the cover sheet and is formed of a hydrophilic material having a large pore structure and wet and dry resiliency to ensure comfort and protection. Coform and air-laid fabric are two materials that are used as the distribution layer.
U.S. Pat. No. 5,533,991 discloses absorbent articles for the applications described which comprise a cover sheet, an absorbent core and a liquid-impermeable baffle. The patentees disclose the use of one or more distribution or transfer layers between the cover sheet and the absorbent core, such layers assisting in keeping the cover dry by directing body fluids downwardly and away from the cover sheet and also to move the body fluids outward in the x and y directions so as to facilitate rapid fluid intake by the absorbent core. The cover sheet is described as including bonded-carded webs and plastic films having a plurality of apertures therein which have a thickness of less than 2 mm, generally between 0.05 and 2 mm. A second material (transfer layer) which is in contact with the cover sheet is provided to distribute fluids from the cover sheet to the absorbent core and these second materials are liquid-permeable nonwoven webs formed from a variety of materials such as polyesters, polyvinyl acetate, cellulose acetate, viscose and so forth. A variety of methods are used to bond the second material to the first material and these include mechanical attachment, adhesives, an ultrasonic bond, thermal bonds and pressure bonds.
H1511 discloses absorbent articles, especially sanitary napkins, containing flow regulators or distribution layers, between the cover sheet and the absorbent core. The patentees report that the absorbent article includes a fluid-pervious cover sheet, a fluid-impervious backsheet joined to the cover sheet and an absorbent core positioned between the cover sheet and the backsheet. The flow regulator is positioned between the cover sheet and the absorbent core and enhances the movement of fluid in the longitudinal direction while controlling movement of fluid in the transverse and Z directions. It is comprised of a plurality of fibers having external capillary channels. The cover sheet is described as an apertured film having a plurality of perforations, e.g., perforated polyethylene. The backsheet is described as a polyethylene film which is impervious to liquids. The absorbent core is described as comprised of common wood pulp sometimes referred to as "air felt" incorporating chemically stiffened and crosslinked cellulosic fibers, peat moss, tissue, etc. To enhance transfer of the fluids through the sanitary napkin the patentees indicate it's important to keep the layers in close or otherwise intimate contact and the contact can be achieved by means of adhesives, ultrasonics and so forth. Adhesives include latex adhesives and hot melt adhesives and may be applied in an open-patterned network of filaments.
U.S. Pat. No. 4,405,310 discloses sanitary napkins incorporating at least two absorbent pads with the lower absorbent pad being secured to the upper pad by means of an adhesive.
U.S. Pat. No. 4,861,652 discloses diapers incorporating a body cover in combination with an absorbent core and liquid-impermeable backsheet. The multi-layered construction of the diaper is held with each layer bonded to one another by thermal or sonic bonds or through the use of adhesives such as hot melt pressure-sensitive adhesives.
U.S. Pat. No. 4,798,604 discloses a water permeable, apertured, contoured polymeric film formed from an elastomer which is suited as a cover for absorbent articles such as sanitary napkins and the like. Two conventional procedures are used in the construction; one being the conventional route of disposing an absorbent material between a liquid-pervious body facing layer (cover sheet) and the fluid-impermeable backing layer (backsheet) and bonding the facing layer and fluid impermeable backing layer at their edges by means of heat sealing thereby enclosing the absorbent material. An alternate method involves bonding the body facing layer to the fluid-impermeable backing layer by means of a hot melt or pressure-sensitive adhesive.